#include <fstream>
using namespace std;

int main(int argc, char *argv[]){
	bool prime[2000000];
	int n,nrPrime = 0;
	ifstream in;
	ofstream out;
	in.open("ciur.in");
	in>>n;
	in.close();
	for(int i = 0;i < n;++i)
		prime[i] = true;
	for(int i = 2;i <= n;++i){
		if(prime[i] == true){
			nrPrime++;
			for(int j = i+i;j <= n;j+=i)
				prime[j] = false;
		}
	}
	out.open("ciur.out");
	out<<nrPrime;
	out.close();
	return 0;
}